This collaborative project involves the use of the resource in bringing FTMS, tandem MS/MS, and theoretical computations to explore the reactivity, isomerisation and fragmentation, structure, and energetics of the radical cation of spiropentane. Previous studies of this ion and substituted variants in condensed phase have reported quantitative conversion to the corresponding radical cation of methylene-cyclobutane. CAD studies involving the preparation of radical cations of spiropentane, methylene-cyclobutane, and other C5H8 isomers with different internal energies indicate that the methylene-cyclobutane radical cation is unique and that the spiropentane radical cation is not quantitatively converted to a single isomer. Ion-molecule reactions with probe molecules, as studied by FTMS, indicate that the radical ion of spiropentane prepared with low internal energy reacts similarly to the radical cation of cyclopropane similarly prepared. Theoretical calculations of th e potential-energy surface of spiropentane radical cation and related isomers show a form that resembles the radical cation of cyclopropane and indicates accessible paths to radical cations of both methylene-cyclobutane and isoprene. This project involves the resource in a role of expanding the knowledge-base of ion-molecule reactions.